Free cutting steel containing small amounts of aluminum and calcium

ABSTRACT

A free cutting steel having excellent mechanical properties, e.g., impact value and good free cutting property and that abrasion amount of used tool is little, in comparison with common Ca free cutting steel, ordinary S free cutting steel and the like which is obtained by adjusting coexisting manner of Ca, S, and Sol.Al in steel.

United States Patent Miyashita et a1.

[ Mar. 7, 1972 [54] FREE CUTTING STEEL CONTAINING SMALL AMOUNTS OF ALUMINUM AND CALCIUM [72] Inventors: Yoshio Miyashita, Kawasaki; Katuhlko Nishikawa, Yokohama; Toslilo Sata, Hoya,

[21] Appl. No.: 26,341

[56] References Cited UNITED STATES PATENTS 422,403 3/1890 l-ladfield ..75/ I 24 1,962,599 6/1934 Keen ..75/124 2,258,604 10/ 1941 Gagnebin ..75/124 Primary Examiner-Hyland Bizot Attorney-Linton &. Linton ABSTRACT A free cutting steel having excellent mechanical properties, e.g., impact value and good free cutting property and that 301 Foreign Application Priorit Data abrasion amount of used tool 15 little, in comparison with com- Apr. 7, 1969 Japan ..45/26l29 mon Ca f ee cutting steel, ordinary S free cutting steel and the like which is obtained by adjusting coexisting manner of Ca, S, Us. and Sol-Al in teel ..C22c 37/10, C22c 39/02 Field of Search ..75/ 123, 124 1 Claims, 1 Drawing Figure 25 o I 0 i1 E O O 3 o o 2 I5 i \l 5 A o Q 8 ta l 0 35 nn u o o 0 0 0.02 0.04 006 0.08 0.10 012 FREE CUTTING STEEL CONTAINING SMALL AMOUNTS F ALUMINUM AND CALCIUM This invention relates to an improved free cutting steel, and more particularly to a Ca free cutting steel showing a low cost, very small abrasion amount of a tool, and stable free cutting property and superior mechanical properties.

It is well known that a steel to which free cutting elements, such as Pb, S. Te or Se are added is employed, and recently Ca is added. It is, however, also known that the steel to which Pb, S, Te or Se are added is costly and its mechanical properties become worse owing to the said addition elements. It is, moreover, discovered that the range of most suitable machining speed wherein improvement of said free cutting property may be expected is narrow comparatively and abrasion amount of used tool in the above range is not always small.

Ca-deoxidation steel is developed to improve the above defects. Speaking about the Ca-deoxidation steel, it will be understood that the making cost is cheaper than that the said steels and the range of said machining speed is considerably broad. It is, however, true that the free cutting property has considerable dispersion and the mechanical properties such impact value and the like become worse. This reason lies in the following matters; generally, some coated layer should be formed on machining face by tool in order to improve free cutting property. There is, in such a case, necessity for controlling SiO which is higher, M 0 which is lower, as composition of oxide system inclusion. For that reason, it is but just that Sol.Al in steel ought to be made lower. Consequently, this method brings about increasing inclusions in steel and inner flaws base on said inclusions and deteriorating mechanical properties as impace value and the like, because of austenite grain size made coarse.

This invention is developed to solve the above-mentioned troubles the features of this invention consist in composition with which Ca, S, and Sol.Al are added to steel simultaneously. That is, this invention steel consists of 0.08 to 0.60% C, 0.15 to 0.60% Si, 0.30 to 2.00% Mn, 0.002 to 0.02% Ca, 0.030 to 0. l 5% S and 0.005 to 0.05% Sol.Al.

An object of this invention is to provide a free cutting steel that abrasion amount of used tool is possible to be caused to grow less easily and stably.

Another object of this invention is to provide a free cutting steel that abrasion amount of tool rake face and also that of tool relief face is possible to be caused to grow little less easily and stably. 7

Further object of this invention is to provide a free cutting steel having excellent mechanical properties, especially impact property.

Other objects and the nature of this invention will become apparent by the following description and the accompanying drawing in which:

The FIGURE illustrates a relation between S content and depth of rake face abrasion.

The above-mentioned composition of this invention steel is decided by the following reasons:

That is, in C content of 0.08 to 0.60%, when said C content is more than 0.60%, toughness and machinability of steel become worse, when said C content is less than 0.08%, the effect of C is impossible to be displayed.

Si and Mn have effects making yield strength and tensile strength of steel increase with low cost. Therefore, a good deal of Si and Mn are added to steel, However, both more than 0.60% Si and more than 2.00% Mn harms toughness of steel. Also, less than 0.15% Si and less than 0.30% Mn has no effect, which is above-mentioned.

Ca content of from 0.002 to 0.02% is effective against said abrasion of tool, because CaO is included in oxide system inclusions and CaS is included in sulfide system inclusion makes machinability of steel worse and less than 0.002% Ca has no effects as mentioned above.

S content of 0.030 to 0.15% is effective in forming CaS- MnS system sulfide, which is effective against said abrasion of tool. More than 0. l 5% S makes said machinability and mechanical properties of steel worse and has a tendency to produce cracks in quenching stage. Less than 0.030% S has no effects as mentioned above.

SoLAl content of 0.005 to 0.05% is provided for deoxidizing and adjusting grain size of steel. More than 0.05% Sol.Al hanns cleanliness of steel and less than 0.005% Sol.Al has no effects as mentioned above.

Stating now about actual examples, the following Table I shows, some chemical compositions of this invention steels, which are A, B, C, D, E and F steel, in comparison with that of other Ca free cutting steels, which are G, H, land J steels. Numeral of an asterisk is out of this invention.

Table II shows results of the above-mentioned steels machined by the following conditions. That is;

Cemented carbide tool; P-20 machining speed; l50m./min.

depth of cut; 2 mm. feed; 0.25 mm./rev. machining time;

10 min.

TABLE II Depth of rake face Height of coated Steels abrasion 4.) layer A 0 0 B 0 I9 D I II .l l l2 Also, the accompanying FIGURE shows relations between S content and depth of rake face abrasion. Such steels are that content of C, Si, Mn and Ca are respectively within the range of this invention steel. The machining conditions are the same data as shown in Table I].

Still more, mechanical properties of steel A and steel 1, which are shown in Table I and Table II and are heattreated with the following conditions.

Water-quenching temperature: 850 C.

Tempering temperature and time: 650 C. X 1 hr.

besides action of a deoxidizing agent. More than 0.02% Ca The results are as shown in Table III.

TABLE III U-noteh Contracchsrpy Yield Tensile Elongation of impact test Austenite point, strength tion area value grain size (kg/mm!) (kg/mm!) (percent) (percent) (kgnL/emfl) number Sol.Al content of the above test steels are dispersed within the range of 0.00l to 0.030%.

It will be well understood from the above-mentioned tables that this invention steel has excellent properties.

According to we inventors studies, it is presumed that the reason lies in being manners of inclusions in this invention steel.

Generally, oxide system inclusions in common Ca free cutting steel having a small amount of sulfur consist of SiO:, CaO and A1 There is, of course, no being of sulfide phase among the same inclusions in the range of low SoLAl content.

0n the contrary, sulfide phase in this invention steel, which consists of CaS and MnS, exists as said oxide phase is wrapped up. It is confirmed that these sulfides, which coexist with said oxides, are effective against harm of said oxides. In such a case, the subject of the above sulfide is CaS and the effect of CaS is kept up even though A1 0 content in oxide phase increases. It is, however, a matter of course that there is the most suitable range in said content of CaS. In this invention,

the more suitable content of CaS is naturally determined by chemical composition of steel, which is as mentioned above. Both common Ca'free cutting steel having low content of S and ordinary S free cutting steel are inferior this invention steel by reason that CaS content of the former is too high and CaS content of the later does not exist.

Thus, Sol.Al content of this invention does not need to be limited to low range like that of common Ca free cutting steel and displays excellent free cutting property. On the contrary, it shows good mechanical properties and is possible to decrease said abrasion amount of tool and to decrease that of 7 tool relief face with case.

What is claimed is:

l. A free cutting steel consisting of 0.08 to 0.60% C; 0.15 to 0.60% Si; 0.30 to 2.00% Mn; 0.002 to 0.02% (Ia; 0.03 to 0.15% S; 0.005 to 0.05% SoLAl, unavoidable impurities and the balance being Fe. 

